1. Field:
The invention is in the field of treatment of smelter flue dusts, refinery sludges, and like metallurgical waste materials containing highly toxic ingredients, for the recovery of copper values.
2. Objective:
In the making of the invention it was a major objective to protect the environment from highly toxic constituents of such waste materials, while recovering copper values therefrom in a more economical manner than theretofore.
3. State of the Art:
It has been proposed heretofore (U.S. Pat. No. 2,686,114) to recover various metal values from ore concentrates high in arsenic by leaching such ore concentrates at elevated temperature (250.degree.-650.degree. F.) and pressure (100-560 psi.) According to the examples given in that patent, use of the specified higher temperatures and pressures results in removal of essentially all of the arsenic values from the leach solution during the leach, resulting in a substantially arsenic-free solution which may be treated in a variety of ways, including cementation techniques, for the recovery of desired metal values, such as copper. The important factor is that there be sufficient iron or alkaline earth metal values present during the leach to render essentially all of the arsenic values insoluble during the leach. This requires the addition of iron or alkaline earth metal values to the leach feed material when the total available therein is less than or even merely the equivalent of the arsenic values present therein.
Unless essentially all of the arsenic values are removed from the solution, common experience in the art indicates that the application of cementation procedures to the resulting pregnant leach solution will be accompanied by the undesirable evolution of arsine gas and that such cementation procedures should be avoided in the absence of essentially complete removal of arsenic values from the leach feed material.